M. F. Silva

Thermoelectric generator and solid-state battery for stand-alone microsystems

This paper presents a thermoelectric (TE) generator and a solid-state battery for powering microsystems. Prototypes of TE generators were fabricatedand characterized. The TE generator is a planar microstructure based on thinfilms of n-type bismuth telluride (Bi 2Te 3) and p-type antimony telluride (Sb 2Te 3), which were deposited using co-evaporation. The measurements on selected samples of Bi 2Te 3and Sb 2Te 3thinfilms indicated a Seebeck coefficient in the range of 90–250 ¹ V K −1 and an in-plane electrical resistivity in the range of 7–17 ¹A m. The measurements also showed TEfigures-of-merit, ZT, at room temperatures (T =300 K) of 0.97 and 0.56, for thinfilms of Bi 2Te 3and Sb 2Te 3, respectively (equivalent to a power factor, PF, of 4.87 mW K −2 m −1 and 2.81 mW K −2 m −1 ). The solid-state battery is based on thinfilms of: an anode of tin dioxide (SnO 2), an electrolyte of lithium phosphorus oxynitride (Li xPO yNz, known as LiPON) and a cathode of lithium cobaltate (LiCoO 2, known as LiCO), which were deposited using the reactive RF (radio-frequency) sputtering. The deposition and characterization results of these thin-films layers are also reported in this paper. (Somefigures in this article are in colour only in the electronic version)

Thin film versus paper-like reduced graphene oxide: Comparative study of structural, electrical, and thermoelectrical properties

We report fabrication of reduced graphene oxide (rGO) films using chemical reduction by hydrazine hydrate and rGO paper-like samples using low temperature treatment reduction. Structural analysis confirms the formation of the rGO structure for both samples. Current-voltage (I–V) measurements of the rGO film reveal semiconductor behavior with the maximum current value of ∼3 × 10−4A. The current for the rGO paper sample is found to be, at least, one order of magnitude higher. Moreover, bipolar resistance switching, corresponding to memristive behavior of type II, is observed in the I–V data of the rGO paper. Although precise values of the rGO film conductivity and the Seebeck coefficient could not be measured, rGO paper shows an electrical conductivity of 6.7 × 102 S/m and Seebeck coefficient of −6 μV/ °C. Thus, we demonstrate a simplified way for the fabrication of rGO paper that possesses better and easier measurable macroscopic electrical properties than that of rGO thin film.

Thin Films for Thermoelectric Applications

The introduction of nanotechnology opened new horizons previously unattainable by thermoelectric devices. The nano-scale phenomena began to be exploited through techniques of thin-film depositions to increase the efficiency of thermoelectric films. This chapter reviews the fundamentals of the phenomenon of thermoelectricity and its evolution since it was discovered in 1822. This chapter also reviews the thermoelectric devices, the macro to nano devices, describing the most used techniques of physical vapor depositions to deposit thermoelectric thin-films. A custom made deposition chamber for depositing thermoelectric thin films by the thermal co-evaporation technique, where construction issues and specifications are discussed, is then presented. All the steps for obtaining a thermoelectric generator in flexible substrate with the custom deposition chamber (to incorporate in thermoelectric microsystems) are described. The aim of thermoelectric microsystem relays is to introduce an energy harvesting application to power wireless sensor networks (WSN) or biomedical devices. The scanning probe measuring system for characterization of the thermoelectric thin films are also described in this chapter. Finally, a few of the prototypes of thermoelectric thin films (made of bismuth and antimony tellurides, \({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}\), and \({\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}\), respectively) obtained by co-evaporation (using the custom made deposition chamber) and characterized for quality assessment are dealt with. All the issues involved in the co-evaporation and characterization are objects of analysis in this chapter.

Stereoscopic image sensor with low-cost RGB filters tunned for the visible range

This paper presents a low-cost technology for fabricating optical filters arrays tuned for the primary colors. The fabrication process presented in this paper is intended for directly printing the optical filters into a transparent flexible substrate (acetate). The target application of these optical filters is for enabling the acquisition of multicolor stereoscopic images with a sensor made in CMOS technology.

A new implantable wireless microsystem to induce mictrition in spinal injury patients

This paper presents a new wireless microsystem for for use in urology. This microsystem is composed by two parts: the electrostimulation and the radio-frequency (RF) subsystems. The electrostimulation part is a silicon box with groves to pass the nerves to be stimulated. Above the stimulation box is putted a cover containing electrodes to do the electrical contacts with the nerves. Using wafer-level packaging (WLP) techniques the RF and the electrostimulation parts are joined together. This implantable microsystem allows the reception of RF signals with user commands to activate the micturition function and the penian erection (on males) patients. The microsystem has an expected area of 5×5 mm2.

433 MHz implantable wireless stimulation of spinal nerves

This paper presents a implantable wireless microsystem concept for operation in the 433 MHz ISM band. The proposed microsystem is composed by two independent subsystems: the electrostimulation and the radio-frequency (RF) subsystems. The electrostimulation part is a silicon box with groves to pass the nerves to be stimulated. The cover of the silicon box contains electrodes for electrical contacting with the nerves. Wafer-level packaging (WLP) techniques will allow the joining of the RF and the electrostimulation subsystems. The target of this implantable microsystem is for RF reception at 433 MHz of user commands to activate the micturition function and the erection (on males) patients. The expected microsystem area will be of 5×5mm2.

Optical filters for narrow-band imaging on medical devices

This paper presents optical filters for narrow-band imaging on medical devices. Two optical filters were designed to provide an extremely narrow passband around the 415 nm (blue) and 540 nm (green) wavelengths using the Fabry-Perot phenomenon. Each filter is composed by successive thin-film layers of dielectric materials of titanium dioxide (TiO2) and silicon dioxide (SiO2). The TiO2 and SiO2 that compose the thin-films were fully characterized by ellipsometry applied within the 250–1700 nm wavelength range. The optical performance of the blue NBI optical filter (415 nm) was also measured. These filters were developed to integrate with light emitting diodes (LED) to provide the desired narrow-band imaging (NBI) bands on medical devices.

A 45° saw-dicing process applied to a glass substrate for wafer-level optical splitter fabrication for optical coherence tomography

This paper reports on the development of a technology for the wafer-level fabrication of an optical Michelson interferometer, which is an essential component in a micro opto-electromechanical system (MOEMS) for a miniaturized optical coherence tomography (OCT) system. The MOEMS consists on a titanium dioxide/silicon dioxide dielectric beam splitter and chromium/gold micro-mirrors. These optical components are deposited on 45° tilted surfaces to allow the horizontal/vertical separation of the incident beam in the final micro-integrated system. The fabrication process consists of 45° saw dicing of a glass substrate and the subsequent deposition of dielectric multilayers and metal layers. The 45° saw dicing is fully characterized in this paper, which also includes an analysis of the roughness. The optimum process results in surfaces with a roughness of 19.76 nm (rms). The actual saw dicing process for a high-quality final surface results as a compromise between the dicing blades grit size (#1200) and the cutting speed (0.3 mm s−1). The proposed wafer-level fabrication allows rapid and low-cost processing, high compactness and the possibility of wafer-level alignment/assembly with other optical micro components for OCT integrated imaging.

NBI Optical Filters in Minimally Invasive Medical Devices

The integration of the narrow band imaging (NBI) technique in highly miniaturized minimally invasive medical devices is presented. NBI provides a more reliable sensing performance for in vivo studies on tissues as compared to approaches based on white light illumination. NBI uses a selective filtered light with peak transmission at 415 (blue) and 540 nm (green). The blue light improves the visualization of the superficial mucosal layer, while the deeper penetration of the green light highlights the vascular patterns of the subepithelial vessels. The optical filters are based on a multilayer thin-film stack, using the Fabry-Perot configuration with titanium dioxide (TiO2) and silicon dioxide (SiO2). The blue light-emitting diode (LED) combined with the blue filter results in a maximum central wavelength at 414 nm, full-width half-maximum (FWHM) of 19 nm and maximum relative transmittance of 21%. The green LED combined with the green filter yields maximum peak intensity at 536 nm, FWHM of 30 nm, and maximum relative transmittance of 35%. RF-sputtering was used for the deposition of NBI optical filters. The refractive index and extinction coefficient of the TiO2 and SiO2 thin films were characterized and the green and blue filter designs were experimentally validated.

A blue optical filter for narrow-band imaging in endoscopic capsules

This paper presents the design, simulation, fabrication, and characterization of a thin-film Fabry-Perot resonator composed of titanium dioxide (TiO2) and silicon dioxide (SiO2) thin-films. The optical filter is developed to be integrated with a light emitting diode (LED) for enabling narrow-band imaging (NBI) in endoscopy. The NBI is a high resolution imaging technique that uses spectrally centered blue light (415 nm) and green light (540 nm) to illuminate the target tissue. The light at 415 nm enhances the imaging of superficial veins due to their hemoglobin absorption, while the light at 540 nm penetrates deeper into the mucosa, thus enhances the sub-epithelial vessels imaging. Typically the endoscopes and endoscopic capsules use white light for acquiring images of the gastrointestinal (GI) tract. However, implementing the NBI technique in endoscopic capsules enhances their capabilities for the clinical applications. A commercially available blue LED with a maximum peak intensity at 404 nm and Full Width Half Maximum (FWHM) of 20 nm is integrated with a narrow band blue filter as the NBI light source. The thin film simulations show a maximum spectral transmittance of 36 %, that is centered at 415 nm with FWHM of 13 nm for combined the blue LED and a Fabry Perot resonator system. A custom made deposition scheme was developed for the fabrication of the blue optical filter by RF sputtering. RF powered reactive sputtering at 200 W with the gas flows of argon and oxygen that are controlled for a 5:1 ratio gives the optimum optical conditions for TiO2 thin films. For SiO2 thin films, a non-reactive RF sputtering at 150 W with argon gas flow at 15 sccm results in the best optical performance. The TiO2 and SiO2 thin films were fully characterized by an ellipsometer in the wavelength range between 250 nm to 1600 nm. Finally, the optical performance of the blue optical filter is measured and presented.